Patent document 1 discloses a variable valve timing device of an internal combustion engine, which is provided with an intermediate lock mechanism that enables a phase of a camshaft relative to a crankshaft to be locked at an intermediate phase.
The intermediate lock mechanism, disclosed in the Patent document 1, has a housing configured to rotate in synchronism with the crankshaft, vanes installed in the housing and configured to rotate together with the camshaft, and a lock pin configured to extend along the direction perpendicular to the camshaft. The intermediate lock mechanism is configured to restrict relative rotation of the camshaft with respect to the crankshaft and hold valve timing at a predetermined intermediate lock position, by inserting the lock pin from the camshaft side into a lock hole formed in the housing.
However, when an engine revolution speed increases and thus a centrifugal force, acting on the lock pin, also increases, there is a possibility that valve timing may not be held at the intermediate lock position by the use of the intermediate lock mechanism.
It is, therefore, in view of the previously-described drawbacks of the prior art, an object of the invention to provide a variable valve timing control device for an internal combustion engine capable of maintaining valve timing at an intermediate lock position even under an operating condition that the valve timing cannot be held at the intermediate lock position by the use of an intermediate lock mechanism owing to an engine revolution speed increase.